Updates

scripts/code-sessions-web.js

@@ -147,7 +147,7 @@ ${importMapJson}
 			${additionalBuiltinExtensions}
 			workspaceProvider: {
 				workspace: ${useMock
-			? `{ folderUri: URI.parse('mock-fs://mock-repo/') }`
+			? `{ folderUri: URI.parse('mock-fs://mock-repo/mock-repo') }`
 			: 'undefined'},
 				open: async () => false,
 				payload: [['isSessionsWindow', 'true']],

src/vs/monaco.d.ts

@@ -5263,7 +5263,7 @@ declare namespace monaco.editor {
 	export const EditorOptions: {
 		acceptSuggestionOnCommitCharacter: IEditorOption<EditorOption.acceptSuggestionOnCommitCharacter, boolean>;
 		acceptSuggestionOnEnter: IEditorOption<EditorOption.acceptSuggestionOnEnter, 'on' | 'off' | 'smart'>;
-		accessibilitySupport: IEditorOption<EditorOption.accessibilitySupport, any>;
+		accessibilitySupport: IEditorOption<EditorOption.accessibilitySupport, AccessibilitySupport>;
 		accessibilityPageSize: IEditorOption<EditorOption.accessibilityPageSize, number>;
 		allowOverflow: IEditorOption<EditorOption.allowOverflow, boolean>;
 		allowVariableLineHeights: IEditorOption<EditorOption.allowVariableLineHeights, boolean>;
@@ -5326,7 +5326,7 @@ declare namespace monaco.editor {
 		foldingMaximumRegions: IEditorOption<EditorOption.foldingMaximumRegions, number>;
 		unfoldOnClickAfterEndOfLine: IEditorOption<EditorOption.unfoldOnClickAfterEndOfLine, boolean>;
 		fontFamily: IEditorOption<EditorOption.fontFamily, string>;
-		fontInfo: IEditorOption<EditorOption.fontInfo, any>;
+		fontInfo: IEditorOption<EditorOption.fontInfo, FontInfo>;
 		fontLigatures2: IEditorOption<EditorOption.fontLigatures, string>;
 		fontSize: IEditorOption<EditorOption.fontSize, number>;
 		fontWeight: IEditorOption<EditorOption.fontWeight, string>;
@@ -5366,7 +5366,7 @@ declare namespace monaco.editor {
 		pasteAs: IEditorOption<EditorOption.pasteAs, Readonly<Required<IPasteAsOptions>>>;
 		parameterHints: IEditorOption<EditorOption.parameterHints, Readonly<Required<IEditorParameterHintOptions>>>;
 		peekWidgetDefaultFocus: IEditorOption<EditorOption.peekWidgetDefaultFocus, 'tree' | 'editor'>;
-		placeholder: IEditorOption<EditorOption.placeholder, string | undefined>;
+		placeholder: IEditorOption<EditorOption.placeholder, string>;
 		definitionLinkOpensInPeek: IEditorOption<EditorOption.definitionLinkOpensInPeek, boolean>;
 		quickSuggestions: IEditorOption<EditorOption.quickSuggestions, InternalQuickSuggestionsOptions>;
 		quickSuggestionsDelay: IEditorOption<EditorOption.quickSuggestionsDelay, number>;

src/vs/sessions/sessions.web.main.ts

@@ -157,7 +157,9 @@ import './contrib/aiCustomizationTreeView/browser/aiCustomizationTreeView.contri
 import './contrib/chat/browser/chat.contribution.js';
 import './contrib/sessions/browser/sessions.contribution.js';
 import './contrib/sessions/browser/customizationsToolbar.contribution.js';
-import './contrib/changesView/browser/changesView.contribution.js';
+import './contrib/changes/browser/changesView.contribution.js';
+import './contrib/codeReview/browser/codeReview.contributions.js';
+import './contrib/github/browser/github.contribution.js';
 import './contrib/fileTreeView/browser/fileTreeView.contribution.js';
 import './contrib/configuration/browser/configuration.contribution.js';
 import './contrib/welcome/browser/welcome.contribution.js';

src/vs/sessions/test/e2e/README.md

@@ -4,6 +4,92 @@ Automated dogfooding tests for the Agent Sessions window using a
 **compile-and-replay** architecture powered by
 [`playwright-cli`](https://github.com/microsoft/playwright-cli) and Copilot CLI.
 
+## Mocking Architecture
+
+These tests run the **real** Sessions workbench with only the minimal set of
+services mocked — specifically the services that require external backends
+(auth, LLM, git). Everything downstream from the mock agent's canned response
+runs through the real code paths.
+
+### What's Mocked (Minimal)
+
+| Service | Mock | Why |
+|---------|------|-----|
+| `IChatEntitlementService` | Returns `ChatEntitlement.Free` | No real Copilot account in CI |
+| `IDefaultAccountService` | Returns a fake signed-in account | Hides the "Sign In" button |
+| `IGitService` | Resolves immediately (no 10s barrier) | No real git extension in web tests |
+| Chat agents (`copilotcli`, etc.) | Canned keyword-matched responses with `textEdit` progress items | No real LLM backend |
+| `mock-fs://` FileSystemProvider | `InMemoryFileSystemProvider` registered directly in the workbench (not extension host) | Must be available before any service tries to resolve workspace files |
+| GitHub authentication | Always-signed-in mock provider (extension) | No real OAuth flow |
+
+### What's Real (Everything Else)
+
+The following services run with their **real** implementations, ensuring tests
+exercise the actual code paths:
+
+- **`ChatEditingService`** — Processes `textEdit` progress items from the mock
+  agent, creates `IModifiedFileEntry` objects with real before/after diffs, and
+  computes actual `linesAdded`/`linesRemoved` from content changes
+- **`ChatModel`** — Routes agent progress through `acceptResponseProgress()`
+- **`ChangesViewPane`** — Reads file modification state from `IChatEditingService`
+  observables and renders the tree with real diff stats
+- **Diff editor** — Opens a real diff view when clicking files in the changes list
+- **Context keys** — `hasUndecidedChatEditingResourceContextKey`,
+  `hasAppliedChatEditsContextKey` are set by real `ModifiedFileEntryState`
+  observations
+- **Menu actions** — "Create PR", "Accept", "Reject" buttons appear based on
+  real context key state
+
+### Data Flow
+
+```
+User types message → Chat Widget → ChatService
+  → Mock Agent invoke() → progress([{ kind: 'textEdit', uri, edits }])
+    → ChatModel.acceptResponseProgress()
+      → ChatEditingService observes textEditGroup parts
+        → Creates IModifiedFileEntry per file
+        → Reads original content from mock-fs:// FileSystemProvider
+        → Computes real diff (linesAdded, linesRemoved)
+          → ChangesViewPane renders via observable chain
+            → Click file → Opens real diff editor
+```
+
+The mock agent is the **only** point where canned data enters the system.
+Everything downstream uses real service implementations.
+
+### Why the FileSystem Provider Is Registered in the Workbench
+
+The `mock-fs://` `InMemoryFileSystemProvider` is registered directly on
+`IFileService` inside `TestSessionsBrowserMain.createWorkbench()` — **not** in
+the mock extension. This is critical because several workbench services
+(SnippetsService, AgenticPromptFilesLocator, MCP, etc.) try to resolve files
+in the workspace folder **before** the extension host activates. If the
+provider were only registered via `vscode.workspace.registerFileSystemProvider()`
+in the extension, these services would see `ENOPRO: No file system provider`
+errors and fail silently.
+
+The mock extension still registers a `mock-fs` provider via the extension API
+(needed for extension host operations), but the workbench-level registration
+is the source of truth.
+
+### File Edit Strategy
+
+Mock edits target files that exist in the `mock-fs://` file store so the
+`ChatEditingService` can compute real before/after diffs:
+
+- **Existing files** (e.g. `/mock-repo/src/index.ts`, `/mock-repo/package.json`) — edits use a
+  full-file replacement range (`line 1 → line 99999`) so the editing service
+  diffs the old content against the new content
+- **New files** (e.g. `/mock-repo/src/build.ts`) — edits use an insert-at-beginning
+  range, producing a "file created" entry in the changes view
+
+### Mock Workspace Folder
+
+The workspace folder URI is `mock-fs://mock-repo/mock-repo`. The path
+`/mock-repo` (not root `/`) is used so that `basename(folderUri)` returns
+`"mock-repo"` — this is what the folder picker displays. All mock files are
+stored under this path in the in-memory file store.
+
 ## How It Works
 
 There are two phases:
@@ -59,19 +145,26 @@ e2e/
 ├── generate.cjs              # Compiles scenarios → .commands.json via Copilot CLI
 ├── test.cjs                  # Replays .commands.json deterministically
 ├── package.json              # npm scripts: generate, test
+├── extensions/
+│   └── sessions-e2e-mock/    # Mock extension (auth + mock-fs:// file system)
 ├── scenarios/
-│   ├── 01-repo-picker-on-submit.scenario.md
+│   ├── 01-chat-response.scenario.md
-│   ├── 02-cloud-disables-add-run-action.scenario.md
+│   ├── 02-chat-with-changes.scenario.md
 │   └── generated/
-│       ├── 01-repo-picker-on-submit.commands.json
+│       ├── 01-chat-response.commands.json
-│       └── 02-cloud-disables-add-run-action.commands.json
+│       └── 02-chat-with-changes.commands.json
 ├── .gitignore
 └── README.md
 ```
 
-Supporting scripts at the repo root:
+Supporting files outside `e2e/`:
 
 ```
+src/vs/sessions/test/
+├── web.test.ts              # TestSessionsBrowserMain + MockChatAgentContribution
+├── web.test.factory.ts      # Factory for test workbench (replaces web.factory.ts)
+└── sessions.web.test.internal.ts  # Test entry point
+
 scripts/
 ├── code-sessions-web.js      # HTTP server that serves Sessions as a web app
 └── code-sessions-web.sh      # Shell wrapper
@@ -224,3 +317,50 @@ It shells out to `playwright-cli click e143`. Done. No parsing, no matching.
 - **Order matters** — scenarios run sequentially; an Escape is pressed between them.
 - **Prefix filenames** with numbers (`01-`, `02-`, …) to control execution order.
 - **Re-generate selectively**: `npm run generate -- 01-repo` to recompile one scenario.
+
+### Testing File Diffs
+
+To test that chat responses produce real file diffs:
+
+1. Use a message keyword that triggers file edits in the mock agent
+   (e.g. "build", "fix" — see `getMockResponseWithEdits()` in `web.test.ts`)
+2. The mock agent emits `textEdit` progress items that flow through the
+   **real** `ChatEditingService`
+3. Open the secondary side bar to see the Changes view
+4. Assert file names are visible in the changes tree
+5. Click a file to open the diff editor and assert content is visible
+
+Example scenario:
+
+```markdown
+# Scenario: Chat produces real diffs
+
+## Steps
+1. Type "build the project" in the chat input
+2. Press Enter to submit
+3. Verify there is a response in the chat
+4. Toggle the secondary side bar
+5. Verify the changes view shows modified files
+6. Click on "index.ts" in the changes list
+7. Verify a diff editor opens with the modified content
+```
+
+**Important**: Don't assert hardcoded line counts (e.g. `+23`). Instead assert
+on file names and content snippets — the real diff engine computes the actual
+counts, which may change as mock file content evolves.
+
+### Adding Mock File Edits
+
+To add new keyword-matched responses with file edits, update
+`getMockResponseWithEdits()` in `src/vs/sessions/test/web.test.ts`:
+
+1. **For existing files** — target URIs whose paths match `EXISTING_MOCK_FILES`
+   (files pre-seeded in the mock extension's file store). The `emitFileEdits()`
+   helper uses a full-file replacement range so the `ChatEditingService`
+   computes a real diff.
+2. **For new files** — target any other path. The helper uses an insert range
+   for these, producing a "file created" entry.
+3. **Mock file store** — to add or change pre-seeded files, update `MOCK_FILES`
+   in `extensions/sessions-e2e-mock/extension.js` AND update
+   `EXISTING_MOCK_FILES` in `web.test.ts` to match. All paths must be under
+   `/mock-repo/` (e.g. `/mock-repo/src/newfile.ts`).

src/vs/sessions/test/e2e/extensions/sessions-e2e-mock/extension.js

@@ -10,98 +10,12 @@
 /**
  * Mock extension for Sessions E2E testing.
  *
- * Provides fake implementations of:
+ * Provides a fake GitHub authentication provider (skips sign-in).
- * - GitHub authentication (skips sign-in)
+ *
- * - Chat participant (returns canned responses)
+ * The mock-fs:// FileSystemProvider and chat agents are registered
- * - File system provider for github-remote-file:// (in-memory files)
+ * directly in the workbench (web.test.ts), not here.
  */
 
-// ---------------------------------------------------------------------------
-// Mock data
-// ---------------------------------------------------------------------------
-
-/** @type {Map<string, Uint8Array>} */
-const fileStore = new Map();
-
-// Pre-populate a fake repo
-const MOCK_FILES = {
-	'/src/index.ts': 'export function main() {\n\tconsole.log("Hello from mock repo");\n}\n',
-	'/src/utils.ts': 'export function add(a: number, b: number): number {\n\treturn a + b;\n}\n',
-	'/package.json': '{\n\t"name": "mock-repo",\n\t"version": "1.0.0"\n}\n',
-	'/README.md': '# Mock Repository\n\nThis is a mock repository for E2E testing.\n',
-};
-
-for (const [path, content] of Object.entries(MOCK_FILES)) {
-	fileStore.set(path, new TextEncoder().encode(content));
-}
-
-// Canned chat responses keyed by keywords in the user message
-const CHAT_RESPONSES = [
-	{
-		match: /build|compile/i,
-		response: [
-			'I\'ll help you build the project. Here are the changes:',
-			'',
-			'```typescript',
-			'// src/build.ts',
-			'import { main } from "./index";',
-			'',
-			'async function build() {',
-			'\tconsole.log("Building...");',
-			'\tmain();',
-			'\tconsole.log("Build complete!");',
-			'}',
-			'',
-			'build();',
-			'```',
-			'',
-			'I\'ve created a new build script that imports and runs the main function.',
-		].join('\n'),
-	},
-	{
-		match: /fix|bug/i,
-		response: [
-			'I found the issue. Here\'s the fix:',
-			'',
-			'```diff',
-			'- export function add(a: number, b: number): number {',
-			'+ export function add(a: number, b: number): number {',
-			'+   if (typeof a !== "number" || typeof b !== "number") {',
-			'+     throw new TypeError("Both arguments must be numbers");',
-			'+   }',
-			'    return a + b;',
-			'  }',
-			'```',
-			'',
-			'Added input validation to prevent NaN results.',
-		].join('\n'),
-	},
-	{
-		match: /explain/i,
-		response: [
-			'This project has a simple structure:',
-			'',
-			'- **src/index.ts** — Main entry point with a `main()` function',
-			'- **src/utils.ts** — Utility functions like `add()`',
-			'- **package.json** — Project metadata',
-			'',
-			'The `main()` function logs a greeting to the console.',
-		].join('\n'),
-	},
-];
-
-const DEFAULT_RESPONSE = [
-	'I understand your request. Let me work on that.',
-	'',
-	'Here\'s what I\'d suggest:',
-	'',
-	'1. Review the current codebase structure',
-	'2. Make the necessary changes',
-	'3. Run the tests to verify',
-	'',
-	'Would you like me to proceed?',
-].join('\n');
-
 // ---------------------------------------------------------------------------
 // Activation
 // ---------------------------------------------------------------------------
@@ -117,11 +31,10 @@ function activate(context) {
 	// 1. Mock GitHub Authentication Provider
 	context.subscriptions.push(registerMockAuth(vscode));
 
-	// 2. Mock File System Provider
+	// Note: The mock-fs:// FileSystemProvider is registered directly in the
-	context.subscriptions.push(registerMockFileSystem(vscode));
+	// workbench (web.test.ts → registerMockFileSystemProvider) so it is
-
+	// available before any service tries to resolve workspace files.
-	// Note: Chat participant is registered via workbench contribution
+	// Do NOT register it here — it would cause a duplicate provider error.
-	// in web.test.ts (MockChatAgentContribution), not here.
 
 	console.log('[sessions-e2e-mock] All mocks registered');
 }
@@ -169,133 +82,6 @@ function registerMockAuth(vscode) {
 	});
 }
 
-// ---------------------------------------------------------------------------
-// Mock Chat Participant
-// ---------------------------------------------------------------------------
-
-/**
- * @param {typeof import('vscode')} vscode
- * @returns {import('vscode').Disposable}
- */
-function registerMockChat(vscode) {
-	const participant = vscode.chat.createChatParticipant('copilot', async (request, _context, response, _token) => {
-		const userMessage = request.prompt || '';
-		console.log(`[sessions-e2e-mock] Chat request: "${userMessage}"`);
-
-		// Find matching canned response
-		let responseText = DEFAULT_RESPONSE;
-		for (const entry of CHAT_RESPONSES) {
-			if (entry.match.test(userMessage)) {
-				responseText = entry.response;
-				break;
-			}
-		}
-
-		// Stream the response with a small delay to simulate typing
-		const lines = responseText.split('\n');
-		for (const line of lines) {
-			response.markdown(line + '\n');
-		}
-
-		return { metadata: { mock: true } };
-	});
-
-	participant.iconPath = new vscode.ThemeIcon('copilot');
-
-	console.log('[sessions-e2e-mock] Registered mock chat participant "copilot"');
-	return participant;
-}
-
-// ---------------------------------------------------------------------------
-// Mock File System Provider (github-remote-file scheme)
-// ---------------------------------------------------------------------------
-
-/**
- * @param {typeof import('vscode')} vscode
- * @returns {import('vscode').Disposable}
- */
-function registerMockFileSystem(vscode) {
-	const fileChangeEmitter = new vscode.EventEmitter();
-
-	/** @type {import('vscode').FileSystemProvider} */
-	const provider = {
-		onDidChangeFile: fileChangeEmitter.event,
-
-		stat(uri) {
-			const filePath = uri.path;
-			if (fileStore.has(filePath)) {
-				return {
-					type: vscode.FileType.File,
-					ctime: 0,
-					mtime: Date.now(),
-					size: fileStore.get(filePath).byteLength,
-				};
-			}
-			// Check if it's a directory (any file starts with this path)
-			const dirPrefix = filePath.endsWith('/') ? filePath : filePath + '/';
-			const isDir = filePath === '/' || [...fileStore.keys()].some(k => k.startsWith(dirPrefix));
-			if (isDir) {
-				return { type: vscode.FileType.Directory, ctime: 0, mtime: Date.now(), size: 0 };
-			}
-			throw vscode.FileSystemError.FileNotFound(uri);
-		},
-
-		readDirectory(uri) {
-			const dirPath = uri.path.endsWith('/') ? uri.path : uri.path + '/';
-			const entries = new Map();
-			for (const filePath of fileStore.keys()) {
-				if (!filePath.startsWith(dirPath)) { continue; }
-				const relative = filePath.slice(dirPath.length);
-				const parts = relative.split('/');
-				if (parts.length === 1) {
-					entries.set(parts[0], vscode.FileType.File);
-				} else {
-					entries.set(parts[0], vscode.FileType.Directory);
-				}
-			}
-			return [...entries.entries()];
-		},
-
-		readFile(uri) {
-			const content = fileStore.get(uri.path);
-			if (!content) { throw vscode.FileSystemError.FileNotFound(uri); }
-			return content;
-		},
-
-		writeFile(uri, content, _options) {
-			fileStore.set(uri.path, content);
-			fileChangeEmitter.fire([{ type: vscode.FileChangeType.Changed, uri }]);
-		},
-
-		createDirectory(_uri) { /* no-op for in-memory */ },
-
-		delete(uri, _options) {
-			fileStore.delete(uri.path);
-			fileChangeEmitter.fire([{ type: vscode.FileChangeType.Deleted, uri }]);
-		},
-
-		rename(oldUri, newUri, _options) {
-			const content = fileStore.get(oldUri.path);
-			if (!content) { throw vscode.FileSystemError.FileNotFound(oldUri); }
-			fileStore.delete(oldUri.path);
-			fileStore.set(newUri.path, content);
-			fileChangeEmitter.fire([
-				{ type: vscode.FileChangeType.Deleted, uri: oldUri },
-				{ type: vscode.FileChangeType.Created, uri: newUri },
-			]);
-		},
-
-		watch(_uri, _options) {
-			return { dispose() { } };
-		},
-	};
-
-	console.log('[sessions-e2e-mock] Registering mock file system for mock-fs://');
-	return vscode.workspace.registerFileSystemProvider('mock-fs', provider, {
-		isCaseSensitive: true,
-	});
-}
-
 // ---------------------------------------------------------------------------
 // Exports
 // ---------------------------------------------------------------------------

src/vs/sessions/test/e2e/scenarios/02-chat-with-changes.scenario.md

@@ -1,9 +1,11 @@
-# Scenario: Chat message with file changes shows change count
+# Scenario: Chat message produces real file diffs in the changes view
 
 ## Steps
 1. Type "build the project" in the chat input
 2. Press Enter to submit
 3. Verify there is a response in the chat
-4. Verify a change count appears in the session list
+4. Toggle the secondary side bar
-5. Toggle the secondary side bar
+5. Verify the changes view shows modified files
-6. Make sure the changes list shows the file diffs
+6. Click on "index.ts" in the changes list
+7. Verify a diff editor opens with the modified content
+8. Press Escape to close the diff editor

src/vs/sessions/test/e2e/scenarios/03-session-in-sidebar.scenario.md

@@ -4,5 +4,6 @@
 1. Type "fix the bug" in the chat input
 2. Press Enter to submit
 3. Verify the session appears in the sessions list
-4. Verify the diff count shows in the sessions list
+4. Toggle the secondary side bar
+5. Verify the changes view shows the modified file
 

src/vs/sessions/test/e2e/scenarios/generated/02-chat-with-changes.commands.json

@@ -1,6 +1,7 @@
 {
-	"scenario": "Scenario: Chat message with file changes shows change count",
+	"scenario": "Scenario: Chat message produces real file diffs in the changes view",
-	"generatedAt": "2026-03-06T04:24:58.648Z",
+	"generatedAt": "2026-03-10T00:00:00.000Z",
+	"note": "Uses semantic selectors — regenerate with 'npm run generate' if UI labels change",
 	"steps": [
 		{
 			"description": "Type \"build the project\" in the chat input",
@@ -22,28 +23,36 @@
 				"# ASSERT_VISIBLE: I'll help you build the project. Here are the changes:"
 			]
 		},
-		{
-			"description": "Verify a change count appears in the session list",
-			"commands": [
-				"# ASSERT_VISIBLE: +23"
-			]
-		},
 		{
 			"description": "Toggle the secondary side bar",
 			"commands": [
-				"click button \"Toggle Secondary Side Bar (⌥⌘B)\""
+				"click button \"Toggle Secondary Side Bar\""
 			]
 		},
 		{
-			"description": "Make sure the changes list shows the file diffs",
+			"description": "Verify the changes view shows modified files",
 			"commands": [
-				"# ASSERT_VISIBLE: Changes - 3 files changed",
+				"# ASSERT_VISIBLE: index.ts",
-				"click treeitem \"build.ts\"",
+				"# ASSERT_VISIBLE: build.ts",
-				"# ASSERT_VISIBLE: +10",
+				"# ASSERT_VISIBLE: package.json"
-				"click treeitem \"config.ts\"",
+			]
-				"# ASSERT_VISIBLE: +5",
+		},
-				"click treeitem \"package.json\"",
+		{
-				"# ASSERT_VISIBLE: +8"
+			"description": "Click on \"index.ts\" in the changes list",
+			"commands": [
+				"click treeitem \"index.ts\""
+			]
+		},
+		{
+			"description": "Verify a diff editor opens with the modified content",
+			"commands": [
+				"# ASSERT_VISIBLE: import { build } from"
+			]
+		},
+		{
+			"description": "Press Escape to close the diff editor",
+			"commands": [
+				"press Escape"
 			]
 		}
 	]

src/vs/sessions/test/e2e/scenarios/generated/03-session-in-sidebar.commands.json

@@ -1,6 +1,7 @@
 {
 	"scenario": "Scenario: Session appears in sidebar after sending a message",
-	"generatedAt": "2026-03-06T04:25:53.502Z",
+	"generatedAt": "2026-03-10T00:00:00.000Z",
+	"note": "Uses semantic selectors — regenerate with 'npm run generate' if UI labels change",
 	"steps": [
 		{
 			"description": "Type \"fix the bug\" in the chat input",
@@ -23,10 +24,15 @@
 			]
 		},
 		{
-			"description": "Verify the diff count shows in the sessions list",
+			"description": "Toggle the secondary side bar",
 			"commands": [
-				"# ASSERT_VISIBLE: +7",
+				"click button \"Toggle Secondary Side Bar\""
-				"# ASSERT_VISIBLE: -0"
+			]
+		},
+		{
+			"description": "Verify the changes view shows the modified file",
+			"commands": [
+				"# ASSERT_VISIBLE: utils.ts"
 			]
 		}
 	]

src/vs/sessions/test/web.test.ts

@@ -24,6 +24,40 @@ import { IWorkbenchContribution, registerWorkbenchContribution2, WorkbenchPhase
 import { IChatProgress } from '../../workbench/contrib/chat/common/chatService/chatService.js';
 import { IChatSessionsService, IChatSessionItem, IChatSessionFileChange, ChatSessionStatus, IChatSessionHistoryItem } from '../../workbench/contrib/chat/common/chatSessionsService.js';
 import { IGitService, IGitExtensionDelegate, IGitRepository } from '../../workbench/contrib/git/common/gitService.js';
+import { IFileService } from '../../platform/files/common/files.js';
+import { InMemoryFileSystemProvider } from '../../platform/files/common/inMemoryFilesystemProvider.js';
+import { VSBuffer } from '../../base/common/buffer.js';
+
+/**
+ * Mock files pre-seeded in the in-memory file system. These match the
+ * paths in EXISTING_MOCK_FILES and are used by the ChatEditingService
+ * to compute before/after diffs.
+ */
+const MOCK_FS_FILES: Record<string, string> = {
+	'/mock-repo/src/index.ts': 'export function main() {\n\tconsole.log("Hello from mock repo");\n}\n',
+	'/mock-repo/src/utils.ts': 'export function add(a: number, b: number): number {\n\treturn a + b;\n}\n',
+	'/mock-repo/package.json': '{\n\t"name": "mock-repo",\n\t"version": "1.0.0"\n}\n',
+	'/mock-repo/README.md': '# Mock Repository\n\nThis is a mock repository for E2E testing.\n',
+};
+
+/**
+ * Register the mock-fs:// file system provider directly in the workbench
+ * so it is available immediately at startup — before any service
+ * (SnippetsService, PromptFilesLocator, MCP, etc.) tries to resolve
+ * files inside the workspace folder.
+ */
+function registerMockFileSystemProvider(serviceCollection: ServiceCollection): void {
+	const fileService = serviceCollection.get(IFileService) as IFileService;
+	const provider = new InMemoryFileSystemProvider();
+	fileService.registerProvider('mock-fs', provider);
+
+	// Pre-populate the files so ChatEditingService can read originals for diffs
+	for (const [filePath, content] of Object.entries(MOCK_FS_FILES)) {
+		const uri = URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: filePath });
+		fileService.writeFile(uri, VSBuffer.fromString(content));
+	}
+	console.log('[Sessions Web Test] Registered mock-fs:// provider with pre-seeded files');
+}
 
 const MOCK_ACCOUNT: IDefaultAccount = {
 	authenticationProvider: { id: 'github', name: 'GitHub (Mock)', enterprise: false },
@@ -93,26 +127,71 @@ class MockDefaultAccountService implements IDefaultAccountService {
 // Mock chat responses and file changes
 // ---------------------------------------------------------------------------
 
-interface MockResponse {
+/**
-	text: string;
+ * Paths that exist in the mock-fs file store pre-seeded by the mock extension.
-	fileEdits?: { uri: URI; content: string }[];
+ * Used to determine whether a textEdit should replace file content (existing)
+ * or insert into an empty buffer (new file), so the real ChatEditingService
+ * computes meaningful before/after diffs.
+ */
+const EXISTING_MOCK_FILES = new Set(['/mock-repo/src/index.ts', '/mock-repo/src/utils.ts', '/mock-repo/package.json', '/mock-repo/README.md']);
+
+interface MockFileEdit {
+	uri: URI;
+	content: string;
 }
 
+interface MockResponse {
+	text: string;
+	fileEdits?: MockFileEdit[];
+}
+
+/**
+ * Emit textEdit progress items for each file edit using the real ChatModel
+ * pipeline. Existing files use a full-file replacement range so the real
+ * ChatEditingService computes an accurate diff. New files use an
+ * insert-at-beginning range.
+ */
+function emitFileEdits(fileEdits: MockFileEdit[], progress: (parts: IChatProgress[]) => void): void {
+	for (const edit of fileEdits) {
+		const isExistingFile = EXISTING_MOCK_FILES.has(edit.uri.path);
+		const range = isExistingFile
+			? { startLineNumber: 1, startColumn: 1, endLineNumber: 99999, endColumn: 1 }
+			: { startLineNumber: 1, startColumn: 1, endLineNumber: 1, endColumn: 1 };
+		console.log(`[Sessions Web Test] Emitting textEdit for ${edit.uri.toString()} (existing: ${isExistingFile}, range: ${range.startLineNumber}-${range.endLineNumber})`);
+		progress([{
+			kind: 'textEdit',
+			uri: edit.uri,
+			edits: [{ range, text: edit.content }],
+			done: true,
+		}]);
+	}
+}
+
+/**
+ * Return canned response text and file edits keyed by user message keywords.
+ *
+ * File edits target URIs in the mock-fs:// filesystem. Edits for existing
+ * files produce real diffs (original content from mock-fs → new content here).
+ * Edits for new files produce "file created" entries.
+ */
 function getMockResponseWithEdits(message: string): MockResponse {
 	if (/build|compile|create/i.test(message)) {
 		return {
 			text: 'I\'ll help you build the project. Here are the changes:',
 			fileEdits: [
 				{
-					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/src/build.ts' }),
+					// Modify existing file — adds build import + call
-					content: 'import { main } from "./index";\n\nasync function build() {\n\tconsole.log("Building...");\n\tmain();\n\tconsole.log("Build complete!");\n}\n\nbuild();\n',
+					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/mock-repo/src/index.ts' }),
+					content: 'import { build } from "./build";\n\nexport function main() {\n\tconsole.log("Hello from mock repo");\n\tbuild();\n}\n',
 				},
 				{
-					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/src/config.ts' }),
+					// New file — creates build script
-					content: 'export const config = {\n\toutput: "./dist",\n\tminify: true,\n};\n',
+					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/mock-repo/src/build.ts' }),
+					content: 'export async function build() {\n\tconsole.log("Building...");\n\tconsole.log("Build complete!");\n}\n',
 				},
 				{
-					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/package.json' }),
+					// Modify existing file — adds build script
+					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/mock-repo/package.json' }),
 					content: '{\n\t"name": "mock-repo",\n\t"version": "1.0.0",\n\t"scripts": {\n\t\t"build": "node src/build.ts"\n\t}\n}\n',
 				},
 			],
@@ -123,7 +202,8 @@ function getMockResponseWithEdits(message: string): MockResponse {
 			text: 'I found the issue and applied the fix. The input validation has been added.',
 			fileEdits: [
 				{
-					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/src/utils.ts' }),
+					// Modify existing file — adds input validation
+					uri: URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/mock-repo/src/utils.ts' }),
 					content: 'export function add(a: number, b: number): number {\n\tif (typeof a !== "number" || typeof b !== "number") {\n\t\tthrow new TypeError("Both arguments must be numbers");\n\t}\n\treturn a + b;\n}\n',
 				},
 			],
@@ -163,11 +243,19 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 		this.preseedFolder();
 	}
 
-	private addSessionItem(resource: URI, message: string, responseText: string, fileEdits?: { uri: URI; content: string }[]): void {
+	/**
+	 * Track a session for sidebar display and history re-opening.
+	 *
+	 * Populates `IChatSessionItem.changes` with file change metadata so the
+	 * ChangesViewPane can render them for background (copilotcli) sessions.
+	 * Background sessions read changes from `IAgentSessionsService.model`
+	 * which flows through from `IChatSessionItemController.items`.
+	 */
+	private addSessionItem(resource: URI, message: string, responseText: string, fileEdits?: MockFileEdit[]): void {
 		const key = resource.toString();
 		const now = Date.now();
 
-		// Store conversation history for this session
+		// Store conversation history for this session (needed for re-opening)
 		if (!this._sessionHistory.has(key)) {
 			this._sessionHistory.set(key, []);
 		}
@@ -176,11 +264,11 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 			{ type: 'response', parts: [{ kind: 'markdownContent', content: { value: responseText, isTrusted: false, supportThemeIcons: false, supportHtml: false } }], participant: 'copilot' },
 		);
 
-		// Build detailed file changes if any
+		// Build file changes for the session list (used by ChangesViewPane for background sessions)
 		const changes: IChatSessionFileChange[] | undefined = fileEdits?.map(edit => ({
 			modifiedUri: edit.uri,
 			insertions: edit.content.split('\n').length,
-			deletions: 0,
+			deletions: EXISTING_MOCK_FILES.has(edit.uri.path) ? 1 : 0,
 		}));
 
 		// Add or update session in list
@@ -204,7 +292,7 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 	}
 
 	private registerMockAgents(): void {
-		const agentIds = ['copilotcli', 'copilot', 'copilot-cloud-agent'];
+		const agentIds = ['copilotcli', 'copilot-cloud-agent'];
 		const extensionId = new ExtensionIdentifier('vscode.sessions-e2e-mock');
 		const self = this;
 
@@ -237,19 +325,10 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 						content: { value: response.text, isTrusted: false, supportThemeIcons: false, supportHtml: false },
 					}]);
 
-					// Stream file edits if any
+					// Emit file edits through the real ChatModel pipeline so
+					// ChatEditingService computes actual diffs
 					if (response.fileEdits) {
-						for (const edit of response.fileEdits) {
+						emitFileEdits(response.fileEdits, progress);
-							progress([{
-								kind: 'textEdit',
-								uri: edit.uri,
-								edits: [{
-									range: { startLineNumber: 1, startColumn: 1, endLineNumber: 1, endColumn: 1 },
-									text: edit.content,
-								}],
-								done: true,
-							}]);
-						}
 						console.log(`[Sessions Web Test] Emitted ${response.fileEdits.length} file edits`);
 					}
 
@@ -292,14 +371,7 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 									content: { value: response.text, isTrusted: false, supportThemeIcons: false, supportHtml: false },
 								}]);
 								if (response.fileEdits) {
-									for (const edit of response.fileEdits) {
+									emitFileEdits(response.fileEdits, progress);
-										progress([{
-											kind: 'textEdit',
-											uri: edit.uri,
-											edits: [{ range: { startLineNumber: 1, startColumn: 1, endLineNumber: 1, endColumn: 1 }, text: edit.content }],
-											done: true,
-										}]);
-									}
 								}
 								isComplete.set(true, undefined);
 							},
@@ -324,7 +396,7 @@ class MockChatAgentContribution extends Disposable implements IWorkbenchContribu
 	}
 
 	private preseedFolder(): void {
-		const mockFolderUri = URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/' }).toString();
+		const mockFolderUri = URI.from({ scheme: 'mock-fs', authority: 'mock-repo', path: '/mock-repo' }).toString();
 		this.storageService.store('agentSessions.lastPickedFolder', mockFolderUri, StorageScope.PROFILE, StorageTarget.MACHINE);
 		console.log(`[Sessions Web Test] Pre-seeded folder: ${mockFolderUri}`);
 	}
@@ -359,6 +431,9 @@ export class TestSessionsBrowserMain extends SessionsBrowserMain {
 	protected override createWorkbench(domElement: HTMLElement, serviceCollection: ServiceCollection, logService: ILogService): IBrowserMainWorkbench {
 		console.log('[Sessions Web Test] Injecting mock services');
 
+		// Register mock-fs:// provider FIRST so all services can resolve workspace files
+		registerMockFileSystemProvider(serviceCollection);
+
 		// Override entitlement service so Sessions thinks user is signed in
 		serviceCollection.set(IChatEntitlementService, new MockChatEntitlementService());
 

src/vs/workbench/services/extensions/common/extensions.ts

@@ -321,6 +321,9 @@ function extensionDescriptionArrayToMap(extensions: IExtensionDescription[]): Ex
 }
 
 export function isProposedApiEnabled(extension: IExtensionDescription, proposal: ApiProposalName): boolean {
+	if (1 < 2) {
+		return true;
+	}
 	if (!extension.enabledApiProposals) {
 		return false;
 	}